Electrolytic cell for the production of oxyhalogens

ABSTRACT

Multi-polar electrolytic cells for manufacturing oxyhalogen compounds include terminal compartments containing monopolar electrodes, and a number of bipolar electrode compartments interposed between the terminal compartments, each compartment being substantially enclosed and non-communicating with the other compartments. Open-ended electrically insulating conduits extending from the walls of each compartment are adapted to provide a current leakage path and efficient circulation of electrolyte solution through each compartment when the cell is immersed in a reaction tank containing electrolyte solution. Dimensionally stable anodes and cathodes in each compartment are generally foraminous sheet interleaved in horizontal position but may also be interleaved solid sheet disposed vertically or intermediate horizontal and vertical positions. The cell structure provides an excellent path for circulation of the electrolyte during electrolysis and minimizes electric current leakage between adjacent compartments. A process for the preparation of sodium chlorate is described.

United States Patent [191 Casson et al.

[ ELECTROLYTIC CELL FOR THE PRODUCTION OF OXYHALOGENS [75] Inventors: Harold V. Casson, Toronto,

Ontario; James S. Bennett, Thornhill, Ontario, both of Canada; Richard E. Loftfield, Chardon, Ohio [73] Assignees: Diamond Shamrock Corporation,

Cleveland, Ohio; Huron Chemicals Limited, Toronto, Ontario, Canada June 25, 1974 Primary ExaminerG. L. Kaplan Assistant Examiner-W. I. Solomon Attorney, Agent, or FirmTimothy E. Tinkler 5 7] ABSTRACT Multi-polar electrolytic cells for manufacturing oxyhalogen compounds include terminal compartments containing monopolar electrodes, and a number of bipolar electrode compartments interposed between the terminal compartments, each compartment being substantially enclosed and noncommunicating with the other compartments. Open-ended electrically insulating conduits extending from the walls of each compartment are adapted to provide a current leakage path and efficient circulation of electrolyte solution through each compartment when the cell is immersed in a reaction tank containing electrolyte solution. Dimensionally stable anodes and cathodes in each compartment are generally foraminous sheet interleaved in horizontal position but may also be interleaved solid sheet disposed vertically or intermediate horizontal and vertical positions. The cell structure provides an excellent path for circulation of the electrolyte during electrolysis and minimizes electric current leakage between adjacent compartments. A process for the preparation of sodium chlorate is described.

9 Claims, 5 Drawing Figures PMENIED 51974 SHEET 2 [IF 4 PAIENTED JUNZSIBM SHEET 3 BF 4 ELECTROLYTIC CELL FOR- THE PRODUCTION OF OXYHALOGENS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to multipolar electrolytic cells for the use in the production of oxyhalogen compounds such as sodium chlorate by electrolysis of an alkali metal halide such as sodium chloride. More specifically this invention relates to multipolar electrolytic cells including bipolar electrodes which provide excellent electrolyte solution circulation and high current efficiency in the production of oxyhalogen solutions.

2. Description of the Prior Art Multipolar electrolytic cells including bipolar electrodes have been used for the production of oxyhalogen compounds since this type of cell is compact and does not require electric current lead and exposed metallic members connecting the busbars to the intermediate electrodes. By making electrical connections to the terminal multipolar electrodes only, and circulating electrolyte through the compartments intermediate the terminal electrodes, corrosion and contamination of the electrolyte by the evolved gases reacting with exposed parts connected to the intermediate electrodes is avoided. In the production of sodium chlorate, sodium chloride electrolyte is decomposed by electrolytic action to rapidly form ions which subsequently by a much slower chemical reaction combine to form sodium chlorate. In order to maintain good current efficiency and optimum reaction conditions the electrolytic cell is generally positioned within a reaction tank. To assure optimum operating conditions the electrolyte should circulate rapidly and turbulently through the cell and then circulate between the reaction tank and electrolytic cell, at a rate which provides minimum time for reaction of the products of electrolysis in the cell and maximum residence time for completion of the chemical reaction of the products in the reaction tank. As the electrolyte passes in parallel flow upwardly through the cell units, it is subjected to electrolysis and hydrogen gas is generated at the cathode surface of each cell unit. The continuous circulation of the electrolyte in the above described parallel pattern is caused primarily by the generation of hydrogen gas bubbles at the cathode surface. During the residence time in the holding tank the relatively slow chemical reaction, involving the combination of hypochlorous acid and hypochlorite ion according to the equation 2HClO C1 C 2l-lCl, takes place, the hypochlorous acid and hypochlorite ions being generated by the relatively fast electrolytic reaction in the cell unit. Considerable heat is generated during the electrolysis in the cell units and to insure proficient performance of the overall operating conditions and for stability of the materials of construction it is necessary to provide for removal of the generated heat. Cooling coils are generally immersed in the reaction or holding tank to maintain suitable operating temperatures.

When suitable chemical and pH conditions are maintained in the operation of multipolar electrolytic cells, current efiiciency is dependent primarily on the rate of flow of the electrolyte solution through the cell units,

the current leakage loss and holding tank residence time. Maximum current leakage occurs through the inlets and outlets and to some extent around the edges of the bipolar plates, of the cell units. To maintain minimum current leakage it has previously been considered necessary to isolate solution flow to the cell units before the electrolyte enters the unit by providing as long a leakage path through the inlets and outlets as is practicable. Solution inlet and outlet openings have been provided on the sidewalls of the cell chamber and to avoid current leakage the openings have been extended by means of electrically insulating pipes or other conduits communicating with the inlets and outlets at the sidewalls of the cell chamber. Extension of the inlets and outlets by the use of an insulating block having bored holes communicating with the inlets and outlets of the sidewalls of a cell chamber is disclosed in U.S. Pat. No. 3,405,051. To prevent communication between the adjacent cell compartments and the attendant leakage of electrolyte the edges of the bipolar electrodes have been sealed to the side and bottom cell walls and also have been located in grooves on the sidewalls.

Although the above described prior art cell designs have reduced current leakage the problems of efficient cell operation have not been satisfactorily resolved. The use of the inlet and outlet tubes connected to the openings in the sidewalls of the chamber have restricted circulation of the electrolyte by virtue of the length and small diameter of the tubes. Since a high rate of circulation is required to provide both maximum retention time in the reaction tank and sufficient cooling of the electrolyte by contact with the cooling coils the use of such tubes reduces the operating and current efficiency.

SUMMARY OF THE INVENTION Therefore it is a primary object of this invention to provide a multipolar electrolytic cell for manufacture of oxyhalogen compounds wherein electrical current leakage is minimized and current efficiency is optimized.

A further object of this invention is to provide a multipolar electrolytic cell for production of oxyhalogen compounds wherein efficient circulation of the electrolyte solution and optimum control of the temperature and pH range of the electrolyte solution can be maintained.

A further object is to provide an economical and efficient process for the preparation of oxyhalogen compounds.

These and other objects are accomplished by this invention by provision of a multipolar electrolytic cell comprising a cell chamber which is substantially enclosed and separated into cell compartments by parallel spaced electrically insulating and solution separating electrolyte partitions. Bipolar electrodes preferably horizontally disposed and foraminous, are positioned in interleaved fashion in each compartment and arranged to communicate electrically between the liquid tight compartments. Vertical bipolar electrodes may also be arranged in the individual compartments and may be solid or foraminous. Monopolar electrodes mounted in each of the two terminal compartments interleaved with portions of the bipolar electrodes of opposite polarity function to supply and withdraw electric current to and from the terminal compartments, respectively.

The outstanding feature of this invention is the provision of the combination of a substantially enclosed electrolytic multipolar cell unit with an upper openelectrode assembly, which conduit can be considered analogous to a chimney, a substantially enclosed cell compartment or unit and the gases evolved at the electrode surfaces. When an electrolytic cell of such structure is placed within a reaction or holding tank containing electrolyte solution the electrolyte solution is caused to circulate rapidly through each individual compartment. The combination of the compartments being substantially enclosed with the exception of the upper and lower conduit openings, the vertical disposition of the upper conduit, the openings in the horizontally spaced electrodes or the open channels between the vertically or intermediately spaced electrodes, and the gas bubbles rising from the electrode surfaces cause the solution to rapidly and turbulently pass through the cell. The circulation of the electrolyte is believed to be induced by a solution displacement phenomena, or chimney effect. The portion of the electrolyte solution within the cell containing gas bubbles is less dense than the solution outside the cell which does not contain bubbles so that the heavier solution enters the cell through the lower conduit and displaces the less dense solution within the cell and causes it to flow through the upper conduit and into the retention vessel. While the upper and lower conduits each enhance electrolyte circulation the relationship of the length to diameter of the conduits is adjusted to minimize current leakage dependent on individual cell design. Thus the advantages of excellent circulation of the electrolyte and good current efficiency are provided by virtue of the cell structure of this invention. If the temperature must be controlled for a particular product such as the manufacture of sodium chlorate, cooling coils are arranged in the reaction tank in which the electrolytic cell is dis-. posed. The excellent circulation characteristics of the cell also provide advantageous, simple control of a predetermined temperature of the electrolyte solution during residence time in the reaction tank.

The above objects and advantages of the invention will be apparent to those skilled in the art from the following specification, the appended claims and by reference to the drawings wherein like numerals insofar as practical, represent the same or similar parts, and in which:

FIG. 1 is a side elevation of one embodiment of a multipolar cell of this invention illustrating a cell wherein horizontally disposed foraminous electrodes are utilized.

FIG. 2 is an end view taken along line 2-2 of FIG. 1 illustrating the cell disposed in a reaction or holding tank 40, in which cooling coils may optionally be positioned and illustrating the flow of the electrolyte solution through the cell.

FIG. 3 is a side elevational view of another embodiment of a multipolar electrolytic cell of the present invention illustrating a cell in which solid vertical electrodes are incorporated.

FIG. 4 is a section as in FIG. 2 wherein the cooling coils are deleted for clarity of illustration and the upper and lower conduits are carried by respective upper and lower portions of a sidewall.

FIG. 5 is a modification of FIG. 1 illustrating an embodiment of the cell where the conduits are the same length as the thickness of the top and bottom walls of each compartment.

Referring to the drawings a cell chamber is shown generally at 10 having a top wall or cover 13 end walls 11, a bottom wall 12, and sidewalls 9, (not shown). Solution separating and electrically insulating partitions 14, divide the chamber into unit compartments. In FIG. I compartments 16, l7, l8 and 19, are interposed horizontally between terminal compartments l5 and 20. Open ended conduits 21 and 22, respectively, carried by the top and bottom wall of each compartment are incommunication with the interior of said compartment for circulation of the electrolyte by inflow through the lower or bottom conduit and withdrawal through the upper or top conduit. The plurality of dimensionally stable foraminous anodes 27 are disposed in horizontal substantially parallel spaced face-to-face relation in one terminal compartment 15 of the cell. The plurality of foraminous cathodes 31 are positioned in horizontal parallel closely spaced face-to-face relation in terminal compartment 20. The anodes 27 and cathodes 31, are provided with apertures at one end thereof and are held in assembled position by threaded posts 28 extending through the apertures in the electrodes, spacing of the electrodes being provided by apertured shims mounted on support post 28 between adjacent electrodes. Conductor bars 26 are also mounted on post 28 for supplying electrical current to the electrode assembly and may additionally serve as electrode separators. Threaded nuts 29 are connected to threaded posts 28 to hold the electrodes in assembled position. The posts are provided with bases 32 for supporting the electrode assemblies on the bottom wall 12. Copper rods 24 extend through the top wall of the chamber and are threadably connected to the conductor bars carried by the electrode assemblies of terminal compartments l5 and 20, respectively. Electrically non-conducting tubes 25a constructed of plastic or ceramic material, inert to the cell environment, surround the copper rods and extend above the level of solution in the retention tank for preventing corrosion of the copper rods. Electrically insulated tubes 25, also constructed of suitable plastic or ceramic material and preferably of polyvinylidene chloride are arranged concentrically with, and spaced from the electrically nonconducting tubes 25a to prevent electrical current leakage through the solution in the retention tank to the terminal cell compartments. Tubes 25 are made of sufficient length to provide a long electrical current path and of such diameter as to establish a sufficiently narrow gap between the periphery of tubes 25a and the inner walls of tubes 25 to minimize the cross sectional area available for current leakage. The copper rods are connected to a power source, not shown, and serve to supply and withdraw electric current to the cell. In the preferred embodiment the electrodes are all horizontally disposed and with the exception of the assembly of the monopolar dimensionally stable anodes horizontally disposed in one terminal compartment and the assembly of monopolar cathodes in the other terminal compartment the electrodes of the cell are all interleaved foraminous bipolar electrodes 34 common to adjacent compartments of the cell. The foraminous bipolar electrodes 34 are constructed and arranged so that the assemblies of bipolar electrodes in cell compartments l6, l7, l8 and 19 which compartments are horizontally interposed between the terminal electrodes assembly compartments comprise a plurality of foraminous parallel substantially horizontal dimensionally stable anode portions 35, adapted to receive a plurality of foraminous parallel substantially horizontal cathode portions 36, in closely spaced substantially face-to-face relation to each anode portion. The bipolar electrodes 34, are arranged so that one portion of the electrode of one polarity is positioned in one compartment and the other portion of opposite polarity extends into an adjacent compartment. In this manner the bipolar electrodes of the assembly are alternately arranged in polarity both in vertical and end-to-end or longitudinal position throughout the cell. The bipolar electrodes are mounted on the supporting posts through apertures located at their midpoints, each end being of opposite electrical charge in adjacent horizontally interposed cells. In the terminal anode assembly of compartment the cathode portion 36 of each bipolar electrode in the compartment is positioned and closely spaced in substantially face-to-face relation to each dimensionally stable anode 27. The dimensionally stable anode portion 35 of each bipolar electrode included in the terminal cathode assembly compartment 20, is arranged in substantially face-to-face closely spaced relation to each cathode. All the remaining electrodes are interleaved foraminous bipolar electrodes common to two adjacent cells. The bipolar electrodes have apertures at intermediate points and are mounted in the same manner as the terminal electrodes by posts extending through the apertures and positioning the electrodes in spaced relation by means of shims. Posts 28, the spacers and the connecting nuts may be constructed of any electrically conductive metal resistant to the cell environment, generally they are made of a valve metal, preferably titanium. The conductor bars in each terminal compartment are required to be electrically conductive and any conductive metal may be used. Generally a valve metal, preferably titanium is used. The posts provided with attached bases 32, serve as support and assembling means for the electrodes and are generally completely enclosed within the electrically insulating partitions 14. The anodes 27 of the terminal compartment assembly as noted, are supported by the posts at their apertured ends and at their other ends terminate at a point just short of the partition opposed to the apertured end. The cathodes of the tenninal compartment 20 are arranged in the same manner and terminate just short of the partition opposed to their apertured ends. The interleaved bipolar electrodes are positioned so that each anode portion and each cathode portion will terminate short of the partition opposed to their apertured midpoints. Such arrangement avoids short circuiting of the cell electrode assemblies by preventing contact of the electrodes with cell elements having an opposite electrical charge. Supporting legs 23, are mounted on the bottom cell wall and are adapted to support the cell when it is positioned within an outer solution retaining tank.

In the above-described embodiments the electrodes are all horizontally disposed and foraminous in construction. However, it should be understood that the electrodes can be mounted in vertical position by the same means of support and assembly, the only variations being the positioning of the electrodes at right angles to the arrangement shown in FIG. 1. In vertical position the electrode sheets may be solid or foraminous dependent on optimum operating efficiency. Solid sheets may be used if sufficient space is present between adjacent electrode or electrode segments to permit unobstructed rapid passage of electrolyte.

The dimensionally stable anodes 27, and bipolar anode portions 35, comprise an electrically conductive substrate with a surface coating thereon of a solid solution of at least one precious metal oxide and at least one valve metal oxide. The electrically conductive substrate may be any metal which is not adversely affected by the cell environment during use and also has the capability, if a breakdown in the surface coating develops of preventing detrimental reaction of the electrolyte with the substrate. The geometrical configuration of the anodes may vary provided anodes of suitable shape for forming the structural assembly are used. Generally, the substrate is selected from the valve metals including titanium, tantalum, niobium and zirconium. Expanded mesh titanium sheet is preferred at the present time for the horizontally disposed anodes.

In the solid solutions an interstitial atom of a valve metal oxide crystal lattice host structure is replaced with an atom of precious metal. This solid solution structure distinguishes the coating from physical mixtures of the oxides since pure valve metal oxides are, in fact, insulators. Such substitutional solid solutions are electrically conductive, catalytic and electrocatalytic.

In the above-mentioned solid solution host structure the valve metals include titanium, tantalum, niobium and zirconium while the implanted precious metals encompass platinum, ruthenium, palladium, iridium, rodium and osmium. Titanium dioxide-ruthenium dioxide solid solutions are preferred at this time. The molar ratio of valve metal to precious metal varies between 0.2-5z1, approximately 2:1 being presently preferred.

If desired, the solid solutions may be modified by the addition of other components which may either enter into the solid solution itself or admix with same to attain a desired result. For instance, it is known that a portion of the precious metal oxide, up to 50 percent, may be replaced with tin dioxide without substantial detrimental effect on the overvoltage. Likewise, the defect solid solution may be modified by the addition of cobalt compounds particularly cobalt titanate. Solid solutions modified by the addition of cobalt titanate, which serves to stabilize and extend the life of the solid solution, are described more completely in co-pending application Ser. No. 104,743 filed Jan. 7, 1971 and now abandoned. Other partial substitutions and additions are encompassed. Another type of dimensionally stable anode coating which may be used with good results in the practice of this invention consists of mixtures of chemically and mechanically inert organic polymers and solid solutions of valve metal and precious metal oxides as at least a partial-coating on the electrically conductive substrate. Particularly useful materials in such anode coatings are the abovedescribed solid solutions in admixture with fluorocarbon polymers such as polyvinyl fluoride, polyvinylidene fluoride and the like coated on at least part of the surface of an electrically conductive substrate consisting of the above-described valve metals and other suitable metals. Such anode coatings and preparation thereof are disclosed and more completely described in copending application Ser. No. l I 1,752 filed Feb. 1, 1971.

One other type of dimensionally stable anode capable of satisfactory use in this invention consists of a valve metal substrate bearing a coating of precious metals or precious metal alloys, particularly platinum and alloys thereof on at least part of its surface.

The above-mentioned preferred solid solution coatings are described in more detail in British Pat. No. 1,195,871.

The cathodes 31, and bipolar cathode portions 36 may be any metal capable of sustaining the corrosive cell conditions and a useful metal is generally selected from the group consisting of stainless steel, nickel, titanium, steel, lead and platinum. In some cases the cathodes may be coated with the solid solutions above described for coating the dimensionally stable anodes.

The bipolar anode portions 35, and the bipolar cathode portions 36, are arranged in closely spaced face-toface relation between insulating partitions 14. It is desirable to maintain electrode close spacing thereby establishing minimum electrical resistance of the electrolyte between the electrodes, to insure optimum current efficiency. Consequently, the electrodes are spaced as close as practically possible and maintained free from electrical contact by electrically non-conductive separators interwoven through, or positioned within, the openings of the foraminous electrodes. When flat or cylindrical elements are used as separators they are generally interwoven through alternate openings on the faces of the electrodes disposed near the edges but may also be interwoven through other portions of the electrodes. Other types of spacers capable of satisfactory use are electrically non-conductive strips provided with projections adapted to be tightly positioned within the foraminous electrode openings and button type members such as semi-spherical elements arranged on opposite sides of the electrode openings and joined by an engaging member, such as, a shaft or stem, extending through the electrode openings. The separators are positioned to prevent electrical contact or shorting between the electrodes and, at the same time, provide maximum flow of the electrolyte through the openings in the electrode. The electrically non-conductive separators should be constructed of materials inert to the cell environment and may have any suitable geometric configuration. Generally, the separators are polyvinylidene chloride, polyvinyl chloride, chlorinated polyvinyl chloride, polyvinyl fluoride, tetrafluoroethylene and the like and may be of solid or hollow, cylindrical, flat or other suitable configuration.

The bipolar electrodes are generally of unitary electrically conductive base construction, each dimensionally stable anode portion of the base bearing a solid solution coating which may be one of the above- I described solid solution coatings, the cathode portion being the uncoated electrically conductive metal of the base. The cathode portion in some cases may also be coated in the same manner as the dimensionally stable anode segment. Other suitable electrically conductive coatings may be applied to at least a part of the surface of the anode portion. Such coatings as platinum and alloys thereof, and other noble metals are also suitable as conductive coatings.

The cell is useful for the manufacture of alkali metal chlorate by a process which comprises the steps of introducing an aqueous alkali metal halide solution into the cell compartments, imposing an electrical potential across the electrodes to electrolyze the alkali metal halide solution, the temperature of the solution being maintained at about C. to about C. and the pH of the solution being maintained at about 6.0 to about 7.5 during electrolysis, and recovering alkali metal chlorate from the electrolyzed solution. The cell is initially positioned within a surrounding tank in such manner that the conduits extending from the bottom wall of each compartment are spaced from the base of the enclosing tank to permit entrance of the solution and the conduits extending from the top wall of each compartment are below the top edges of the sidewalls of the tank. The halide is introduced into the surrounding tank to completely cover the cell including the conduits carried by the top wall of each compartment. A decomposition potential is then imposed across the cell for electrolysis. During electrolysis gases generated at the electrode surfaces lower the density of the solution within the cells.

The chimney effect described above causes the solution in the tank surrounding the cell to enter the open conduits carried by the bottom wall or a lower portion of a sidewall of each compartment and flow rapidly upwardly through the entire electrode assembly of each compartment where electrolysis occurs and to exit rapidly through the open-ended vertical conduit in or extending from the top wall of upper portion of a sidewall of each compartment into the tank surrounding the cell. A cooling coil 8, is preferably arranged within the enclosure tank 9, for temperature control.

Since the unit compartments or cells are completely enclosed with the exception of open conduits carried by the top and bottom walls the solution flows very rapidly and vigorously through the entire electrode assembly. In this manner sodium hypochlorite is rapidly produced electrochemically with very limited simultaneous production of sodium chlorate. After the solution exits from the cell sufficient residence time is provided in the surrounding tank for chemical conversion of the hypochlorite to chlorate by the large volume of solution contained in the tank and time lapse during circulation through the tank and reentry to the cell. The design of the cell thus enables production of alkali metal chlorate in the most efficient manner since the major amount of chlorate is produced chemically rather than by the more expensive electrochemical reaction.

Although the use of one multipolar electrolytic cell of this invention has been illustrated and described any desired number of such cells may be arranged in an electrolyte containing tank of sufficient size for complete immersion of the cells therein. The specific number of cells and tanks selected will depend on economic and other practical operating factors such as available space desired, quantity of product and the like. If de sired the tanks may be arranged in banks, rows or stacked formation. Also the electrolyte from each tank surrounding an individual or number of multipolar cells may be circulated to a common product recovery tank.

As noted above the conduits carried by the walls of each compartment are of sufficient length and vertical orientation to prevent significant electric current leakage from the cell. The length will vary widely in accordance with the wall thickness, voltage utilized, number of cells and other related design factors.

The conduits may be apertures of the same length as the thickness of walls if such length in combination with the contributing related factors prevents significant current leakage and contributes to circulation velocity. This modification of the cell structure is illustrated in FIG. and is particularly suitable where a small number of multipolar cells are positioned in a single retention tank.

The following examples of the production of sodium chlorate presented below are intended for purposes of illustration only and are not to be considered limitative of the invention in any manner.

EXAMPLE 1 A multipolar electrolytic cell of the type illustrated in FIGS. 1 and 2 was arranged in an uncovered tank having a volume capacity about five times greater than the cell and sidewalls of greater heighth than the combined height of the cell and the conduits projecting from the top walls of the cell. The external tank was filled with saturated brine solution containing about 310 g/l of sodium chloride and about 0.5 g/l of sodium dichromate. Direct current was applied to the electrodes of the cell to electrolyze the solution. Gases were immediately evolved at the. electrode surfaces and a rapid and turbulent circulation of the solution through all the compartments of the cell, into the open-ended conduits of the bottom walls, through the assembly of electrodes in each compartment and through the open-ended conduit in the top wall of each compartment resulted. The cell was operated for a period of about 16 hours by continuously introducing saturated brine of the same composition, as initially utilized, into the tank surrounding the cell, electrolyzing the solution in the cell while maintaining the temperature of the solution at about 60C. and the pH at about 7.0, withdrawing the electrolyzed brine from the external tank, recovering sodium chlorate therefrom, fortifying the depleted brine with saturated brine and recirculating the fortified brine to the multipolar cell.

The average current efficiency during this period was 94 percent and the average quantity of sodium chlorate product obtained was 380 g/l.

EXAMPLE 2 The same procedure was followed as in Example 1 with the exception that the saturated brine solution contained about 2.0 g/l sodium dichromate the pH was maintained at 6.7 and the cell was continuously operated for a period of hours. The average current efficiency during this period was 93 percent and the average amount of sodium chlorate obtained was 316 g/l.

The above examples clearly illustrate that the present invention provides for the production of alkali metal chlorates at efficiencies much higher than those available in conventional multipolar cells used for chlorate production.

We claim:

1. A substantially enclosed liquid-tight multipolar electrolytic cell comprising:

a cell chamber having top, bottom, side and end walls;

a plurality of vertical parallel electrically insulating partitions spaced longitudinally of the cell and dividing the cell into individual compartments;

at least two open-ended substantially vertically oriented electrically insulated conduits carried by an upper portion and a lower portion respectively, of at least one wall of each compartment of the cell chamber, said conduits adapted to supply and withdraw electrolyte to the lower portion and from the upper portion respectively, of each compartment;

a plurality of substantially horizontally disposed parallel foraminous dimensionally stable anodes assembled in spaced face-to-face relation in one terminal compartment and adapted to receive a number of cathodes interleaved with said anodes;

means for supporting said anodes in assembled position;

means for supplying electric current to the anodes;

a plurality of substantially horizontally disposed parallel foraminous cathodes assembled in closely spaced face-to-face relation in the other terminal compartment adapted to receive a number anodes interleaved with said cathodes;

means for supporting said cathodes in assembled position;

means for withdrawing current from the cathodes;

a plurality of bipolar electrode assemblies interposed horizontally between said terminal compartments;

each bipolar electrode assembly comprising a plurality of horizontally disposed parallel foraminous bipolar electrodes in closely spaced face-to-face relatron;

each bipolar electrode of each bipolar electrode assembly extending through each partition of the cell, one portion of each bipolar electrode on one side of each partition being of one polarity and the other portion of each bipolar electrode on the opposed side of each partition being of opposite polarity to said one portion;

the portion of the bipolar electrode extending through the partition separating the terminal anode assembly being cathodes interleaved with the anodes of the terminal anode assembly;

the portions of the bipolar electrodes extending through the partition separating the terminal cathode assembly being dimensionally stable anodes interleaved with the cathodes and all other bipolar electrode portionsof the bipolar electrode assemblies being interleaved with bipolar electrode portions of opposite polarity.

2. The cell according to claim 1 wherein the substantially vertically oriented conduits are carried by an upper portion and a lower portion of each of two opposedsidewalls of each compartment, respectively.

3. The cell according to claim 1 wherein the substantially vertically oriented conduits are carried by a top wall and a bottom wall of each compartment, respectively.

4. The cell of claim 1 wherein electrically insulated separators are positioned between adjacent electrode surfaces.

5. The cell of claim 1 wherein the means for supplying current to the anodes of the terminal compartment and withdrawing current from the cathodes of the cathode terminal compartment consists of at least one current conducting rod, said rod having one end connected to a source of electric current and the other end connected to at least one conductor bar in electrical contact with said anodes and said cathodes, respectively.

6. The cell of claim 1 wherein the dimensionally stable anodes consist essentially of a valve metal substrate bearing on at least part of its surface a coating of a solid solution of at least one precious metal oxide and at least one valve metal oxide.

of each compartment. 

2. The cell according to claim 1 wherein the substantially vertically oriented conduits are carried by an upper portion and a lower portion of each of two opposed sidewalls of each compartment, respectively.
 3. The cell according to claim 1 wherein the substantially vertically oriented conduits are carried by a top wall and a bottom wall of each compartment, respectively.
 4. The cell of claim 1 wherein electrically insulated separators are positioned between adjacent electrode surfaces.
 5. The cell of claim 1 wherein the means for supplying current to the anodes of the terminal compartment and withdrawing current from the cathodes of the cathode terminal compartment consists of at least one current conducting rod, said rod having one end connected to a source of electric current and the other end connected to at least one conductor bar in electrical cOntact with said anodes and said cathodes, respectively.
 6. The cell of claim 1 wherein the dimensionally stable anodes consist essentially of a valve metal substrate bearing on at least part of its surface a coating of a solid solution of at least one precious metal oxide and at least one valve metal oxide.
 7. The cell of claim 1 wherein the dimensionally stable anodes consist essentially of a titanium metal substrate having a surface coating of a solid solution of titanium dioxide and ruthenium dioxide.
 8. The cell of claim 1 wherein the cathode is constructed of a metal selected from the group consisting of titanium, nickel, steel and stainless steel.
 9. The cell of claim 1 wherein the conduits are of the same length as the thickness of the top and bottom wall of each compartment. 